1. Field of the Invention
The present invention relates to a golfing iron club having a shaft attached to a head formed by forging and provided with a face on a front surface and a shaft connecting portion on one side, and a manufacturing method thereof.
2. Description of the Related Art
Golf clubs which comprise a head and a shaft, are generally classified as one of three types: a wood, an iron, or a putter. Irons are classified by the loft angle of their head. Irons with a small loft angle (for example, from 20 to 30 degrees) are called xe2x80x9clong ironsxe2x80x9d, while irons with a large loft angle (for example, from 40 to 50 degrees) are called xe2x80x9cshort ironsxe2x80x9d. Normally, irons are numbered in ascending order from longest to shortest, for example, Nos. 1, 2, 3, 4, 5, 6, 7, 8, 9 and PW (pitching wedge).
The head of an iron club may have a concave back (a cavity-back iron) on the rear of the face which is the front of the head for hitting golf balls, or may have a smooth back (a solid-back iron). The front has an area known by such names as xe2x80x9cthe sweet spotxe2x80x9d.
When manufacturing the aforementioned head, the usual method, for reasons of strength, is forging. The material conventionally used for the head is soft iron. After forging the soft iron to form the head piece, the head is subject to heat treatment and other processing followed by surface polishing, etc., until the final product is formed.
To realize high strength however, soft iron has recently begun to be replaced by high-strength metals such as stainless steel, titanium alloys, and nickel alloys. At the same time, because of improvements with dies, the shape of cavity-back forged heads of irons has been changing from a comparatively small and flat cavity base area, to a range of designs such as a large cavity base area with an irregular surface, while a deeply gouged design known as an xe2x80x9cunder cutxe2x80x9d is also used.
Although high-strength metals can be used to manufacture superior heads, they have a drawback. High-strength metals offer high strength even at high temperatures but with little ductility. When such high-strength metal heads with large and deep cavities and in various designs are forged, the metal does not expand sufficiently to achieve the desired shape, resulting in underfill. If efforts are made to force the desired shape, then fracturing or deformation occur.
Thus, with conventional manufacture by forging, forging processes such as rolling, preforming, intermediate forming and finishing, are implemented gradually to form the head. However, forming the head exclusively by forging processes using dies results in fracturing and other problems during forging, and not only is the number of processing stages increased but also die costs and other costs rise. In the manufacture of the abovementioned cavity-back iron head in particular, the cavity-back iron head can be formed into roughly the same shape as the abovementioned solid-back by forging, and subsequent machining can create the cavity portion, but this method includes such problems as substantial materials wastage, and further machining stages to finish the head to a complex shape.
The present invention address the above-mentioned problems, with the object of providing a method of manufacturing a golfing iron club with a head of metal material, where the head is formed precisely and inexpensively.
According to a first aspect of the present invention there is provided a method of manufacturing a golfing iron club having a shaft attached to a head formed by forging and provided with a face on a front surface, a cavity in a rear surface, and a shaft connecting portion on one side, which comprises the steps of: forming a raw material of the head, selected from among stainless steel, titanium alloy, nickel alloy and high tensile strength steel, into a head piece so that the head piece may be provided with respective parts corresponding to said face, shaft connecting portion and cavity, by a first die forging step; forming a lower peripheral face of the part corresponding to said cavity, by a first machining step, while cutting off flash formed during the first die forging step; forming the head piece into said head, by a second die forging step; and forming the lower peripheral face of the part corresponding to said cavity to an undercut shape.
With the construction of the first aspect, the head may be formed by machining between the pre- and post-forging stages, whereby even though a high strength metallic material is used, there can be provided a golfing iron club whose head has a wide and deep cavity with various and complicated designs, and yet is formed precisely and inexpensively. Further, although the configuration of flash varies per respective products, the post-forging, i.e., the second forging step can be performed precisely without being affected by the flash, due to the flash being cut off prior to the post-forging step.
According to another aspect of the present invention there is provided a method of manufacturing a golfing iron club according to the foregoing aspect, wherein said first and second machining steps use an end mill as a machining tool, in which an end mill of a smaller diameter is used in said second machining step than in said first machining step.
With the end mill of a smaller diameter used for the post-machining, more precise processing is possible, thus obtaining a finish with more precisely adjusted distribution of weight.
The invention is also addressed to a golfing iron club manufactured by the methods.
Other objects, features and advantages of the invention will become apparent to those skilled in the art, from the following description of the preferred embodiments of the invention, wherein reference is made to the accompanying drawings, in which: